The disclosures herein relate generally to flexible leaflet prosthetic heart valves and more particularly to a wire stented valve including posts having a lengthened trajectory.
Heart valves, of the tissue type and the flexible polymer type, require a stent that deflects under load, yet remains below a design stress. In fact, the lower the stress, the better the fatigue resistance. An objective, therefore, is a structure with a high ratio of stent flexibility to stent stress. Another objective is to stay within the tight anatomical envelope of the aorta.
Various stented valve devices have been proposed. U.S. Pat. No. 4,106,129 discloses a supported bioprosthetic heart valve in which the supporting stent is capable of annular deformation and also of limited perimetric expansion and contraction during heart operation. The stent includes a wire frame composed of a single flexible wire preformed to define inverted U-shaped commissure supports merging smoothly with arcuate portions connecting such supports.
In U.S. Pat. No. 4,343,048, a stent for a cardiac valve comprises a base ring having metal legs projecting therefrom in a generally axial direction, each leg being flexible in such a manner that, when the stent has a valve installed therein and the valve is under pressure such as when operating in the heart, each respective leg can resiliently deform over substantially its whole axial length to take up strain in the valve without impairing its performance.
U.S. Pat. No. 4,501,030 discloses a prosthetic heart valve including a frame having a plurality of commissure supports, a plurality of resilient supports, and a plurality of valve leaflets. The valve leaflets are attached to the resilient supports, and the resilient supports lie radially outwardly of the commissure supports, respectively. When in use, the valve is subjected to forces which are used to clamp the valve leaflets between the resilient supports and the commissure supports to augment whatever other leaflet attachment techniques may be used.
U.S. Pat. No. 5,037,434 discloses a bioprosthetic heart valve comprising first and second mechanisms for supporting leaflets to provide multiple effective spring constants. An inner frame supporting commissures of the valve is elastic, permitting the commissures to bend in toward the center of the prosthetic heart valve at very low loads. A relatively rigid annular support ring supports the elastic frame and provides the second spring constant mechanism. An attachment system for sewing bioprosthetic leaflets to the frame and clamping the leaflets between the frame and the annular ring minimizes stress risers in the leaflets. The leaflets have an uncoupled mating edge where the leaflets meet in the center of the valve. The uncoupled portions of the leaflets permit the leaflets to roll by each other.
U.S. Pat. No. 5,545,215 discloses a frame to be placed as an external support of a biological valved conduit containing three leaflets. This external frame, made of biocompatible metal or plastic is sutured to the outer surface of the valved conduit made of biological or biocompatible membrane or sigmoid valve root in order to maintain its natural geometry. The frame has a general cylindrical configuration, circular as viewed from above and below. From a side view however, both upper and lower ends of the cylinder present three convex curvatures joined at equidistant points of the circumference. These upper and lower curves are joined by three vertical struts, so that three large saddle shaped paraboloid gaps result. The frame is a wire-like structure.
U.S. Pat. No. 5,562,729 discloses a multi-leaflet heart valve composed of biocompatible polymer which simultaneously imitates the structure and dynamics of biological heart valves. The valve includes a plurality of flexible leaflets dip cast on a mandrel. The leaflets are then bonded with a bonding agent to the interior surfaces of a plurality of struts on a metal-reinforced prosthetic stent. The leaflets open and close in response to the pumping action of the heart.
To improve the flexibility of a wire stent, a thinner or finer wire can be used. Flexibility will be increased, but so will the maximum stress encountered in the stent. Conversely, to reduce the stresses in a wire stent, a thicker wire can be used but flexibility is sacrificed. A wire stent with a crimp collar is analogous to a thickened section, and flexibility of the stent is lost adjacent the crimp collar.
A flat pattern stent can reduce stress by use of larger sections at regions of high stress. However, flexibility is also reduced. In fact, the highest flexibility is achieved with a uniform cross-section. Thinning a section locally effectively increases the remaining sections.
Flexibility can be increased by increasing the stent height, but this has the potential of interfering with aortic anatomy. Similarly, increasing the diameter of the valve will increase flexibility, but is not suitable for small aortas. Changing materials is also an option but medically acceptable alloys are limited.
Therefore, what is needed is a stent with a uniform cross-section and a high ratio of stent flexibility to stent stress.
One embodiment, accordingly, provides a stent with uniform cross-section, lengthened trajectory and a high ratio of stent flexibility to stent stress. To this end, a stent includes an elongated stent member having a plurality of flexible post members. Each post member includes a pair of opposite sides. A first end of each post member has an apex which interconnects the opposite sides. A second end of each post member is an open end. The opposite sides are angled to converge toward each other at the second end.
A principal advantage of this embodiment is that, a stent may be provided with a high ratio of stent flexibility to stent stress while remaining within the prescribed valve envelope.